Fault detection for battery management systems

ABSTRACT

A battery management system includes multiple sensors, status detection circuitry, and fault detection circuitry. The sensors sense statuses of a battery pack. The status detection circuitry detects whether the battery pack is in a normal condition based on the statuses to generate a detection result. The fault detection circuitry detects whether a fault is present in the battery pack. The sensors include a current sensor that senses a battery current of the battery pack. The fault detection circuitry includes a detection circuit that monitors a rate of change of a voltage at a terminal of the battery pack, and detects whether a fault is present in the current sensor based on a result of a comparison between the rate of change and a threshold and based on the detection result.

RELATED APPLICATION

This application is a Continuation Application of the co-pendingcommonly-owned U.S. Patent Application with Ser. No. 16/058,218, filedon Aug. 8, 2018, which claims benefit under 35 U.S.C. § 119(a) toApplication No. 1713274.7, now Patent No. 2551081, filed with the UnitedKingdom Intellectual Property Office on Aug. 18, 2017, herebyincorporated herein by reference in its entirety.

BACKGROUND

FIG. 1 illustrates a circuit diagram of a conventional battery pack 100.The battery pack 100 includes battery cells 102, a battery managementsystem (hereinafter, BMS) 104, and sensors such as a sense resistorR_(SEN) and a thermistor R_(THM). The sense resistor R_(SEN) generates asense voltage V_(SEN) indicative of a current flowing through thebattery cells 102. The thermistor R_(THM) generates an indicationvoltage V_(THM) indicative of the temperature in the battery pack 100.The BMS 104 protects the battery pack 100 from, e.g., an over-currentcondition, an over-temperature condition, an under-temperaturecondition, etc., based on the sensed information, e.g., V_(SEN) andVTHM, from the sensors. However, if the sensors and the BMS 104 are notwell connected or if the sensors are broken, then the BMS 104 cannotreceive correct information from the sensors, and this may place thebattery pack 100 and/or a system load powered by the battery pack 100 ata high risk of being damaged.

Additionally, the BMS 104 includes a voltage regulator (not shown) thatgenerates a regulated output to power internal function blocks and/orperipherals such as a microcontroller unit (MCU), an LED (light-emittingdiode) display, LDO (low dropout) regulator, etc. If a fault (e.g., ashort circuit) is present in the components powered by the voltageregulator, it can draw excessive current from the voltage regulator andgenerate heat to damage the BMS 104 and/or the battery pack 100.

SUMMARY

Embodiments according to the present invention detect faults in thestatus sensors and battery management system of a battery pack.

In embodiments, a battery management system includes multiple sensors,status detection circuitry, and fault detection circuitry. The sensorssense statuses of a battery pack. The status detection circuitry detectswhether the battery pack is in a normal condition based on the statusesto generate a detection result. The fault detection circuitry detectswhether a fault is present in the battery pack. The sensors include acurrent sensor that senses a battery current of the battery pack. Thefault detection circuitry includes a detection circuit that monitors arate of change of a voltage at a terminal of the battery pack, anddetects whether a fault is present in the current sensor based on aresult of a comparison between the rate of change and a threshold andalso based on the detection result.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of embodiments of the claimed subject matterwill become apparent as the following detailed description proceeds, andupon reference to the drawings, wherein like numerals depict like parts,and in which:

FIG. 1 illustrates a circuit diagram of a conventional battery pack.

FIG. 2A illustrates a circuit diagram of an example of a battery pack,in an embodiment of the present invention.

FIG. 2B illustrates a circuit diagram of an example of a batterymanagement system, in an embodiment of the present invention.

FIG. 3 illustrates examples of signal waveforms for a battery pack, inan embodiment of the present invention.

FIG. 4 illustrates a circuit diagram of an example of a detectioncircuit, in an embodiment of the present invention.

FIG. 5A illustrates a circuit diagram of an example of a detectioncircuit, in an embodiment of the present invention.

FIG. 5B illustrates a circuit diagram of an example of a detectioncircuit, in an embodiment of the present invention.

FIG. 6 illustrates an example of a method for detecting whether a shortcircuit is present in a current sensor, in an embodiment of the presentinvention.

FIG. 7 illustrates an example of a method for detecting whether a shortcircuit is present in a current sensor, in an embodiment of the presentinvention.

FIG. 8 illustrates an example of a method for detecting whether an opencircuit is present at a sensing pin coupled to a current sensor, in anembodiment of the present invention.

FIG. 9 illustrates an example of a method for detecting a fault in atemperature sensor, in an embodiment of the present invention.

FIG. 10 illustrates a circuit diagram of an example of a battery pack,in an embodiment of the present invention.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentinvention. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims.

Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will berecognized by one of ordinary skill in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

Embodiments according to the present invention provide solutions todetect faults in battery packs. When a fault in a status sensor or in abattery management system (BMS) in a battery pack is detected, then anaction such as fixing the fault, replacing the defective sensor with anew sensor, replacing the defective BMS with a new BMS, replacing thedefective battery pack with a new battery pack, or the like can be takento protect the battery pack and/or a system load powered by the batterypack. As a result, the risk of the battery pack and/or the system loadbeing damaged can be reduced.

FIG. 2A illustrates a circuit diagram of an example of a battery pack200, in an embodiment of the present invention. As shown in FIG. 2A, thebattery pack 200 includes one or more battery cells 202, a batterymanagement system (BMS) 204, and status sensors such as a current sensor258 and a temperature sensor 260. The status sensors can sense statusesof the battery pack 200. The BMS 204 includes status detection circuitry262 that detects whether the battery pack 200 is in a normal conditionbased on the sensed statuses. The BMS 204 also includes fault detectioncircuitry 264 that detects whether a fault is present in the statussensors.

More specifically, in an embodiment, the current sensor 258, e.g., asense resistor R_(SEN), senses a battery current I_(BAT) (e.g., acharging current or a discharging current) of the battery cells 202 togenerate a sense voltage V_(SEN) indicative of the battery currentI_(BAT). The temperature sensor 260, e.g., a thermistor R_(THM), sensestemperature in the battery pack 200 to generate an indication voltageV_(THM) indicative of the temperature.

In an embodiment, the BMS 204 can be an integrated circuit (IC) thatincludes current sensing pins ISP and ISN that receive a sense voltageV_(SEN) from the current sensor 258 through a low-pass filter 224. Thestatus detection circuitry 262 receives the sense voltage V_(SEN) fromthe current sensing pins ISP and ISN, and determines whether the batterycurrent I_(BAT) is greater than or less than an over-current (OC)threshold according to the sense voltage V_(SEN). If the battery currentI_(BAT) is greater than the OC threshold, then the status detectioncircuitry 262 determines that the battery current I_(BAT) is in an OCcondition. If the battery current I_(BAT) is less than the OC threshold,then the status detection circuitry 262 determines that the batterycurrent I_(BAT) is in a normal condition.

Additionally, in an embodiment, the BMS 204 includes a temperaturesensing pin PA0 that receives an indication voltage V_(THM) from thetemperature sensor 260. The status detection circuitry 262 receives theindication voltage V_(THM) from the temperature sensing pin PA0, anddetermines a temperature status of the battery pack 200. For example,the temperature sensor 260 includes a thermistor R_(THM) having anegative temperature coefficient, and when a preset constant currentflows through the thermistor R_(THM), the indication voltage V_(THM) candecrease if the temperature increases, and increase if the temperaturedecreases. Thus, if the indication voltage V_(THM) is less than anover-temperature threshold V_(VOT), then the status detection circuitry262 determines that the battery pack 200 is in an over-temperaturecondition. If the indication voltage V_(THM) is greater than anunder-temperature threshold V_(UT) (V_(UT)>V_(OT)), then the statusdetection circuitry 262 determines that the battery pack 200 is in anunder-temperature condition. If the indication voltage V_(THM) isgreater than the over-temperature threshold V_(OT) and less than theunder-temperature threshold V_(UT), then the status detection circuitry262 determines that the battery pack 200 is in a normal temperaturecondition.

In an embodiment, the BMS 204 also includes a voltage sense pin V_(PACK)that senses a terminal voltage V_(PACK) at the positive input/outputterminal PACK+of the battery pack 200. Additionally, the BMS 204 mayinclude sensing pins VS and VD that receive a voltage across anR_(DS(ON)) resistance of the discharge switch Q_(DSG) of the batterypack 200. In other words, the sensing pins VS and VD can receive adrain-source voltage V_(DS) of the discharge switch Q_(DSG) when thedischarge switch Q_(DSG) (e.g., a metal-oxide-semiconductor field-effecttransistor; MOSFET) operates in a linear (ohmic) region, e.g., is fullyturned on. The fault detection circuitry 264 can detect whether a faultis present in the status sensors based on the sense voltage V_(SEN),voltages at the pins ISP and ISN, the indication voltage V_(THM), theterminal voltage V_(PACK), and/or the drain-source voltage V_(DS). Forexample, the fault detection circuitry 264 can detect whether a shortcircuit is present in the current sensor 258 based on the sense voltageV_(SEN) and a rate of change of the terminal voltage V_(PACK), and/orthe drain-source voltage V_(DS). The fault detection circuitry 264 canalso detect whether an open circuit is present between the statusdetection circuitry 262 and the current sensor 258 based on the voltagesof the pins ISP and ISN. Moreover, the fault detection circuitry 264 candetect whether a short circuit or an open circuit is present in thetemperature sensor 260 based on the indication voltage V_(THM). Detailedexplanations for the fault detection are presented as follows.

FIG. 2B illustrates a circuit diagram of an example of the BMS 204, inan embodiment of the present invention. FIG. 2B is described incombination with FIG. 2A, FIG. 3, FIG. 4, FIG. 5A, FIG. 5B, FIG. 6, FIG.7, FIG. 8 and FIG. 9. As shown in FIG. 2B, the BMS 204 includes acontrol logic circuit 226, a status detection circuit 262′, and a faultdetection circuit 264′. The status detection circuit 262′ can includedetection circuits 212 and 216. The fault detection circuit 264′ caninclude detection circuits 208, 218 and 214.

In an embodiment, the combined circuit of the dV_(PACK)/dt detectioncircuit 208 and the control logic circuit 226 can be referred to as a“first detection circuit,” and the first detection circuit can detect ashort circuit in the current sensor 258. In an embodiment the combinedcircuit of the V_(RDS(ON)) detection circuit 218 and the control logiccircuit 226 can be referred to as a “second detection circuit,” and thesecond detection circuit can detect a short circuit in the currentsensor 258. In an embodiment, the combined circuit of the (V_(R1),V_(R2)) detection circuit 214, the current generating circuits 220 and222, and the control logic circuit 226 can be referred to as a “thirddetection circuit,” and the third detection circuit can detect an opencircuit at the pins ISP and ISN. In an embodiment, the combined circuitof the V_(THM) detection circuit 216 and the control logic circuit 226can be referred to as a “fourth detection circuit,” and the fourthdetection circuit can detect a short circuit and/or an open circuit inthe temperature sensor 260.

In an embodiment, the status detection circuit 262′ and the controllogic circuit 226 constitute the status detection circuitry 262 (FIG.2A) that detects statuses of the battery pack 200 based on informationfrom the status sensors 258 and 260. More specifically, the statusdetection circuit 262′ includes a battery-current (_(IBAT)) detectioncircuit 212. An example of the battery-current detection circuit 212 isillustrated in FIG. 4. For clarity, the filter capacitors in thelow-pass filter 224 shown in FIG. 2B are not shown in FIG. 4.

In the example of FIG. 4, the battery-current detection circuit 212includes a comparator 452 that compares a voltage differenceV_(ISN)-V_(ISP) between the sensing pins ISN and ISP with a voltagethreshold V_(OC) to generate a comparison result 230, e.g., a digitallogic signal. In an embodiment, the comparison result 230 can bereferred to as a “detection result” of the status detection circuit262′. The voltage threshold Voc can represent an OC threshold I_(OC) ofthe battery current I_(BAT). In an embodiment, as shown in FIG. 4, thecurrent generating circuits 220 and 222 generate currents I₁ and I₂ toflow through the resistors R₁ and R₂, to maintain the voltages at thesensing pins ISP and ISN at positive voltage levels, e.g., greater thanground voltage. In an embodiment, the resistors R₁ and R₂ havesubstantially the same resistance, and the currents I₁ and I₂ havesubstantially the same current level. Thus, when the currents I₁ and I₂flow through the resistors R₁and R₂ respectively, the voltage differenceV_(ISN)-V_(ISP) between the sensing pins ISN and ISP is substantiallyequal to the sense voltage V_(SEN) across the current sensor 258, andthe comparison result 230 can also represent a result of the comparisonbetween the sense voltage V_(SEN) and the voltage threshold V_(OC). Thecontrol logic circuit 226 can determine whether the battery currentI_(BAT) is in an OC condition or a normal condition according to thecomparison result 230. For example, if the comparison result 230indicates that the sense voltage V_(SEN) is not greater than the voltagethreshold V_(OC), then the control logic circuit 226 can determine thatthe battery current I_(BAT) is not greater than the OC threshold I_(OC)and is in the normal condition; otherwise, the control logic circuit 226can determine that the battery current I_(BAT) is greater than the OCthreshold I_(OC) and is in the OC condition.

In an embodiment, “the resistors R₁ and R₂ have substantially the sameresistance” mentioned above means a resistance difference between theresistors R₁ and R₂ is permissible as long as the resistance differenceis relatively small and can be neglected. “The currents I₁ and I₂ . . .have substantially the same current level” mentioned above means a leveldifference between the currents I₁ and I₂ is permissible as long as thelevel difference is relatively small and can be neglected.

Although, in the example of FIG. 4, the battery-current detectioncircuit 212 includes a comparator 452, the invention is not so limited.In another embodiment, the battery-current detection circuit 212 caninclude a differential amplifier and an analog-to-digital converter(ADC). The amplifier and ADC can convert the voltage differenceV_(ISN)-V_(ISP) (or the sense voltage V_(SEN)) to a digital signalindicative of the battery current I_(BAT). The control logic circuit 226can compare the digital signal with a reference (e.g., indicative of thevoltage threshold V_(OC)) to determine whether the battery currentI_(BAT) is in an OC condition or a normal condition.

Returning to FIG. 2B, the status detection circuit 262′ can also includea temperature detection circuit 216. The temperature detection circuit216 can include an ADC that converts an indication voltage V_(THM) onthe temperature sensor 260 to a digital signal 232 indicative of thebattery temperature. The control logic circuit 226 can compare thedigital signal 232 with respective references (e.g., indicative of theover-temperature threshold V_(OT) or under-temperature threshold V_(UT))to determine whether the battery temperature is in a normal-temperaturecondition, an over-temperature condition, or an under-temperaturecondition.

In an embodiment, the fault detection circuit 264′, the temperaturedetection circuit 216, and the control logic circuit 226 constitute thefault detection circuitry 264 that detects faults in the status sensors258 and 260. By way of example, the fault detection circuit 264′ caninclude a rate-of-change (dV_(PACK)/dt) detection circuit 208 thatmonitors a rate of change of a terminal voltage V_(PACK) (e.g.,represented by dV_(PACK)/dt or ΔV_(PACK)/Δt) at the positive terminalPACK+ of the battery pack 200. The control logic circuit 226 can obtaininformation 238 for the rate of change dV_(PACK)/dt from therate-of-change detection circuit 208, and compare the rate of changedV_(PACK)/dt with a predetermined first threshold TH1 (which may also bereferred to as a rate of change threshold). Moreover, the control logiccircuit 226 can detect whether a fault is present in the current sensor258 based on a result of a comparison between the rate of changedV_(PACK)/dt and the first threshold TH1 and based on a detection result230 provided by the battery-current detection circuit 212. In anembodiment, the rate of change dV_(PACK)/dt can have a negative value,and the “the rate of change dV_(PACK)/dt” used herein therefore means anabsolute value |dV_(PACK)/dt| of the rate of change.

More specifically, in an embodiment, when the battery pack 200 ispowering a system load, the battery current I_(BAT) (e.g., a dischargingcurrent) can increase if the system load absorbs more power, and candecrease if the system load absorbs less power. If an overload conditionoccurs in the system load or if a short circuit is present between theterminals PACK+ and PACK− of the battery pack 200, then the batterycurrent I_(BAT) can increase quickly. In an embodiment, the PCB (printedcircuit board) trace 240 between the battery cells 202 and the positiveterminal PACK+ includes parasitic inductance 242 and parasiticresistance 244. Additionally, the battery cells 202 include internalresistance 246. Thus, if the battery current I_(BAT) flowing through theparasitic inductor 242, the parasitic resistance 244, and the internalresistance 246 increases quickly, it can increase voltage drops acrossthe parasitic inductor 242, the parasitic resistance 244, and theinternal resistance 246 quickly, and this can result in decreasing theterminal voltage V_(PACK) at the positive terminal PACK+ quickly. In anembodiment, if a rate of change dV_(PACK)/dt (e.g., a rate of decrease)of the terminal voltage V_(PACK) is greater than the first threshold TH1for a predetermined time interval AΔt_(PRE), it can indicate that thebattery current I_(BAT) is in an over-current condition, and the statusdetection circuitry can detect the over-current condition by receiving arelatively large sense voltage V_(SEN) from the current sensor 258.However, if the current sensor 258 is short-circuited, then the statusdetection circuitry may receive a relatively small sense voltage V_(SEN)(e.g., zero volts) and determine that the battery current I_(BAT) is ina normal condition. Thus, in an embodiment, if the abovementioned firstdetection circuit (e.g., including the circuits 208 and 226) detectsthat the rate of change dV_(PACK)/dt is greater than the first thresholdTH1 for a predetermined time interval Δt_(PRE), and the status detectioncircuitry detects that the battery current I_(BAT) is in a normalcondition, then the first detection circuit determines that a shortcircuit is present in the current sensor 258.

FIG. 3 illustrates examples of signal waveforms for a battery currentI_(BAT) and a terminal voltage V_(PACK) of the battery pack 200, in anembodiment of the present invention. FIG. 3 is described in combinationwith FIG. 2A and FIG. 2B. As shown in FIG. 3, the waveform 302represents an example of the battery current I_(BAT), e.g., adischarging current, of the battery pack 200, and the waveform 304represents an example of the terminal voltage V_(PACK) at the positiveterminal PACK+ of the battery pack 200.

In the example of FIG. 3, from time t0 to t1, the discharging currentI_(BAT) remains at a relatively stable level, and the terminal voltageV_(PACK) decreases slowly as the voltage V_(BAT) of the battery cells202 decreases. At time t1, the discharging current I_(BAT) increasesquickly (e.g., because of an overload condition or a short circuitbetween terminals PACK+ and PACK−) and increases to greater than an OCthreshold I_(CC), e.g., at time t2. Accordingly, the terminal voltageV_(PACK) (e.g., represented by the solid line 306 in waveform 304)decreases at a rate greater than the first threshold TH1 (e.g.,represented by the dashed line TH1 in waveform 304), and this situationcan last for at least a predetermined time interval Δt_(PRE).

Returning to FIG. 2B, the battery pack 200 includes a discharge switchQ_(DSG) that the battery current I_(BAT) can flow through. When thedischarge switch Q_(DSG) (e.g., a MOSFET) operates in a linear (ohmic)region, e.g., is fully turned on, the discharge switch Q_(DSG) has anR_(DS(ON)) resistance, and a sense voltage V_(RDS(ON)) across theR_(DS(ON)) resistance (e.g., a drain-source voltage V_(DS)) canrepresent the battery current I_(BAT). In an embodiment, if the sensevoltage V_(RDS(ON)) is greater than a predetermined second threshold TH2(which may also be referred to as a sense voltage threshold) for apreset time interval, it indicates that the battery current I_(BAT) isin an OC condition. Thus, the second detection circuit (e.g., includingthe V_(RDS(ON)) detection circuit 218 and the control logic circuit 226)can monitor the sense voltage V_(RDS(OS)) across the discharge switchQ_(DSG), and can detect whether a fault (e.g., a short circuit) ispresent in the current sensor 258 based on a result of the comparisonbetween the sense voltage V_(RDS(OS)) and the second threshold TH2, andalso based on a result of the detection performed by the statusdetection circuitry 262. By way of example, if the second detectioncircuit detects that the sense voltage V_(RDS(ON)) is greater than thesecond threshold TH2 for a preset time interval, and the statusdetection circuitry 262 detects that the battery current I_(BAT) is in anormal condition, e.g., the status detection circuitry receives arelatively small sense voltage V_(SEN) (e.g., zero volts) from thecurrent sensor 258, then the second detection circuit determines that ashort circuit is present in the current sensor 258.

FIG. 5A illustrates a circuit diagram of an example of theabovementioned third detection circuit 500A, in an embodiment of thepresent invention. As shown in FIG. 5A, the third detection circuit 500Aincludes the (V_(R1), V_(R2)) detection circuit 214, current generatingcircuits 220 and 222, and the control logic circuit 226. FIG. 5A isdescribed in combination with FIG. 2A, FIG. 2B and FIG. 4.

As shown in FIG. 5A, a first resistor R₁ (e.g., a resistor in thelow-pass filter 224 in FIG. 2B) is coupled between a first end E1 of thecurrent sensor 258 and a first terminal ISP of the status detectioncircuitry, and a second resistor R₂ (e.g., a resistor in the low-passfilter 224 in FIG. 2B) is coupled between a second end E2 of the currentsensor 258 and a second terminal ISN of the status detection circuitry.The current generating circuit 220 generates a first current I₁ throughthe first resistor R₁ from the first terminal ISP to the first end E1,and the current generating circuit 222 generates a second current I₂through the second resistor R₂ from the second terminal ISN to thesecond end E2. In an embodiment, the resistances R₁ and R₂ can berelatively small, and the currents I₁ and I₂ can also be relativelysmall. Thus, if the first terminal ISP is well-connected to the firstend E1 through the first resistor R₁, then a voltage V_(R1) on the firstresistor R₁ can be relatively small (e.g., less than a third thresholdTH3, which may also be referred to as a first voltage threshold).Similarly, if the second terminal ISN is well-connected to the secondend E2 through the second resistor R₂, then a voltage V_(R2) on thesecond resistor R₂ can be relatively small (e.g., less than a fourththreshold TH4, which may also be referred to as a second voltagethreshold). However, if an open circuit is present at the first terminalISP (e.g., the status detection circuitry has a loose connection withthe first end E1 of the current sensor 258), then a voltage V_(ISP) atthe first terminal ISP can be pulled up by the power supply V_(PULL),e.g., V_(ISP)=V_(PULL). As a result, the voltage V_(R1) on the firstresistor R₁ can increase to greater than the third threshold TH3.Similarly, if an open circuit is present at the second terminal ISN,then the voltage V_(R2) on the second resistor R₂ can increase togreater than the fourth threshold TH4.

Accordingly, the third detection circuit can detect whether a fault(e.g., an open circuit) is present at the first and second terminals ISPand ISN by comparing a voltage V_(R1) on the first resistor R₁ with thepredetermined third threshold TH3 and by comparing a voltage V_(R2) onthe second resistor R₂ with the predetermined fourth threshold TH4. Byway of example, in the (V_(R1), V_(R2)) detection circuit 214 shown inFIG. 5A, a comparator 570 compares the voltage V_(R1) with the thirdthreshold TH3 to generate an output 228 indicative of the comparisonresult, and a comparator 572 compares the voltage VR2 with the fourththreshold TH4 to generate an output 268 indicative of the comparisonresult. The control logic 226 receives the outputs 228 and 268. If theoutput 228 indicates that the voltage V_(R1) on the first resistor R₁ isgreater than the third threshold TH3, then the control logic 226determines that an open circuit is present at the first terminal ISP.Similarly, if the output 268 indicates that the voltage V_(R2) on thesecond resistor R₂ is greater than the fourth threshold TH4, then thecontrol logic 226 determines that an open circuit is present at thesecond terminal ISN.

FIG. 5B illustrates a circuit diagram of an example of theabovementioned third detection circuit 500B, in an embodiment of thepresent invention. FIG. 5B is described in combination with FIG. 2A,FIG. 2B, FIG. 4 and FIG. 5A.

In the example of FIG. 5B, the comparator 570 includes a switch Q₁(e.g., a MOSFET) and a current generating circuit 520. The firstresistor R₁ can be coupled between the gate and source terminals of theswitch Q₁ such that a voltage V_(R1) on the first resistor R₁ controls agate-source voltage of the switch Q₁. In an embodiment, the thirdthreshold TH3 includes a turn-on threshold of the switch Q₁. If thevoltage VR1 on the first resistor R₁ is less than the third thresholdTH3, then the switch Q₁ i is turned off and the output 228 can be logichigh. If the voltage V_(R1) on the first resistor R₁ is greater than thethird threshold TH3, then the switch Q₁ is turned on and the output 228can be logic low. As a result, the logic level of the output 228 canindicate whether an open circuit is present at the first terminal ISP.

Similarly, the comparator 572 can include a switch Q₂ (e.g., a MOSFET)and a current generating circuit 522. The second resistor R₂ can becoupled between the gate and source terminals of the switch Q₂ such thata voltage V_(R2) on the second resistor R₂ controls a gate-sourcevoltage of the switch Q₂. In an embodiment, the fourth threshold TH4includes a turn-on threshold of the switch Q₂. If the voltage V_(R2) onthe second resistor R₂ is less than the fourth threshold TH4, then theswitch Q₂ is turned off and the output 268 can be logic high. If thevoltage V_(R2) on the second resistor R₂ is greater than the fourththreshold TH4, then the switch Q₂ is turned on and the output 268 can belogic low. As a result, the logic level of the output 268 can indicatewhether an open circuit is present at the second terminal ISN.

Returning to FIG. 2B, in an embodiment, the abovementioned fourthdetection circuit (e.g., including the temperature detection circuit 216and the control logic circuit 226) detects whether a fault is present inthe temperature sensor 260 (e.g., a thermistor R_(THM)) by comparing anindication voltage V_(THM) on the temperature sensor 260 with a fifththreshold TH5 and a sixth threshold (which may also be referred to asindication voltage thresholds). The fifth threshold TH5 is less than theover-temperature threshold V_(UT), and the sixth threshold TH6 isgreater than the under-temperature threshold V_(UT). More specifically,as mentioned above, in an embodiment, when the battery pack 200 is in anormal temperature condition, the indication voltage V_(THM) is greaterthan the over-temperature threshold V_(OT) and less than theunder-temperature threshold V_(UT)(V_(UT)>V_(OT)). If a short circuit ispresent in the thermistor R_(THM), then the indication voltage V_(THM)can be dragged down by the ground, e.g., zero volts, to less than theover-temperature threshold V_(OT). Thus, if the fourth detection circuitdetects that the indication voltage V_(THM) is less than the fifththreshold TH5 (e.g., TH5<V_(OT)) for a specified time interval, then thefourth detection circuit determines that a short circuit is present inthe thermistor R_(THM). On the other hand, if an open circuit is presentin the thermistor R_(THM), then the indication voltage V_(THM) can bepulled up by an internal voltage to greater than the under-temperaturethreshold V_(UT). Thus, if the fourth detection circuit detects that theindication voltage V_(THM) is greater than a sixth threshold TH6 (e.g.,TH6>V_(UT)) for a specified time interval, then the fourth detectioncircuit determines that an open circuit is present in the thermistorR_(THM).

FIG. 6 illustrates a flowchart 600 of an example of a method fordetecting whether a short circuit is present in the current sensor 258,in an embodiment of the present invention. FIG. 6 is described incombination with FIG. 2A, FIG. 2B, FIG. 3 and FIG. 4. Although specificsteps are disclosed in FIG. 6, such steps are examples for illustrativepurposes. That is, embodiments according to the present invention arewell-suited to performing various other steps or variations of the stepsrecited in FIG. 6. In an embodiment, operations in the flowchart 600 canbe performed by the abovementioned first detection circuit (e.g.,including the rate-of-change detection circuit 208 and the control logiccircuit 226).

By way of example, at step 602, the rate-of-change detection circuit 208monitors a rate of change dV_(PACK)/dt of a terminal voltage V_(PACK) atthe positive terminal PACK+ of the battery pack 200, and generates asignal 238 indicative of the rate of change dV_(PACK)/dt.

At step 604, the control logic circuit 226 compares the rate of changedV_(PACK)/dt with the first threshold TH1. If the rate of changedV_(PACK)/dt is greater than the first threshold TH1, then the flowchart600 goes to step 606; otherwise, it returns to step 602.

At step 606, if the control logic circuit 226 detects that the rate ofchange dV_(PACK)/dt is greater than the first threshold TH1 for apredetermined time interval Δt_(PRE), then the flowchart 600 goes tostep 608; otherwise, it goes to step 604.

At step 608, the control logic circuit 226 receives a comparison result230 from the battery-current detection circuit 212 and determineswhether an OC condition is present in the battery pack 200. If thecontrol logic circuit 226 determines that an OC condition is present inthe battery pack 200, then the flowchart 600 goes to step 612;otherwise, it goes to step 610.

At step 612, the control logic circuit 226 determines that no shortcircuit is present in the current sensor 260.

At step 610, the control logic circuit 226 determines that a shortcircuit is present in the current sensor 260.

FIG. 7 illustrates a flowchart 700 of an example of a method fordetecting whether a short circuit is present in the current sensor 258,in an embodiment of the present invention. FIG. 7 is described incombination with FIG. 2A, FIG. 2B and FIG. 4. Although specific stepsare disclosed in FIG. 7, such steps are examples for illustrativepurposes. That is, embodiments according to the present invention arewell-suited to performing various other steps or variations of the stepsrecited in FIG. 7. In an embodiment, operations in the flowchart 700 canbe performed by the abovementioned second detection circuit (e.g.,including the V_(RDS(ON)) detection circuit 218 and the control logiccircuit 226).

More specifically, at step 702, the V_(RDS(ON)) detection circuit 218monitors a sense voltage V_(RDS(OS)) across the R_(DS(ON)) resistance ofthe discharge switch Q_(DSG) and generates a signal 236 (FIG. 2B)indicative of the sense voltage V_(RDS(ON)).

At step 704, the control logic circuit 226 receives the signal 236 todetermine whether the sense voltage V_(RDS(OS)) is greater than thesecond threshold TH2. If the sense voltage V_(RDS(ON)) is greater thanthe second threshold TH2, then the flowchart 700 goes to step 706;otherwise, it returns to step 702.

At step 706, if the control logic circuit 226 detects that the sensevoltage V_(RDS(ON)) is greater than the second threshold TH2 for apreset time interval, then the flowchart 700 goes to step 708;otherwise, it goes to step 704.

At step 708, the control logic circuit 226 receives a comparison result230 from the battery-current detection circuit 212 and determineswhether an OC condition is present in the battery pack 200. If thecontrol logic circuit 226 determines that an OC condition is present inthe battery pack 200, then the flowchart 700 goes to step 712;otherwise, it goes to step 710.

At step 712, the control logic circuit 226 determines that no shortcircuit is present in the current sensor 260.

At step 710, the control logic circuit 226 determines that a shortcircuit is present in the current sensor 260.

In an embodiment, the BMS 204 can detect whether a short circuit ispresent in the current sensor 258 by performing the method in FIG. 6. Inanother embodiment, the BMS 204 can detect whether a short circuit ispresent in the current sensor 258 by performing the method in FIG. 6 incombination with the method in FIG. 7. For example, if the control logiccircuit 226 detects that the rate of change dV_(pack)/dt is greater thanthe first threshold TH1 for a predetermined time interval Δt_(PRE) andthe sense voltage V_(RDS(OS)) is greater than the second threshold TH2for a preset time interval, and the control logic circuit 226 detectsthat the battery pack 200 is in a normal condition, then the controllogic circuit 226 determines that a short circuit is present in thecurrent sensor 258.

FIG. 8 illustrates a flowchart 800 of an example of a method fordetecting whether an open circuit is present at a sensing pin ISP or ISNcoupled to the current sensor 258, in an embodiment of the presentinvention. FIG. 8 is described in combination with FIG. 2A, FIG. 2B,FIG. 4, FIG. 5A and FIG. 5B. Although specific steps are disclosed inFIG. 8, such steps are examples for illustrative purposes. That is,embodiments according to the present invention are well-suited toperforming various other steps or variations of the steps recited inFIG. 8. In an embodiment, operations in the flowchart 800 can beperformed by the abovementioned third detection circuit (e.g., includingthe (V_(R1), V_(R2)) detection circuit 214, the current generatingcircuits 220 and 222, and the control logic circuit 226).

More specifically, at step 802, the current generating circuits 220 and222 generate substantially identical currents I₁ and I₂ to flow throughthe filter resistors R₁ and R₂, respectively.

At step 804, the (V_(R1), V_(R2)) detection circuit 214 monitors avoltage V_(R1) on the first filter resistor R₁ and a voltage V_(R2) onthe second filter resistor R₂.

For example, at step 806, the comparator 570 (e.g., including thecurrent generating circuit 520 and the switch Q₁) compares the voltageV_(R1) on the first filter resistor R₁ with the third threshold TH3 togenerate an output 228. If the output 228 indicates that the voltageV_(R1) on the first filter resistor R₁ is greater than the thirdthreshold TH3, then the flowchart 800 goes to step 808; otherwise, itgoes to step 804.

At step 808, the control logic circuit 226 determines that an opencircuit is present at the first terminal ISP.

For another example, at step 810, the comparator 572 (e.g., includingthe current generating circuit 522 and the switch Q₂) compares thevoltage V_(R2) on the second filter resistor R₂ with the fourththreshold TH4 to generate an output 268. If the output 268 indicatesthat the voltage V_(R2) on the second filter resistor R₂ is greater thanthe fourth threshold TH4, then the flowchart 800 goes to step 812;otherwise, it goes to step 804.

At step 812, the control logic circuit 226 determines that an opencircuit is present at the second terminal ISN.

FIG. 9 illustrates a flowchart 900 of an example of a method fordetecting a fault in the temperature sensor 260, in an embodiment of thepresent invention. FIG. 9 is described in combination with FIG. 2A andFIG. 2B. Although specific steps are disclosed in FIG. 9, such steps areexamples for illustrative purposes. That is, embodiments according tothe present invention are well-suited to performing various other stepsor variations of the steps recited in FIG. 9. In an embodiment,operations in the flowchart 900 can be performed by the abovementionedfourth detection circuit (e.g., including the detection circuit 216 andthe control logic circuit 226).

More specifically, at step 902, the temperature detection circuit 216monitors an indication voltage V_(THM) from the temperature sensor 260to generate a signal 232 indicative of the indication voltage V_(THM),e.g., indicative of the temperature of the battery pack 200.

At step 904, the control logic circuit 226 obtains information for theindication voltage V_(THM) from the signal 232, and compares theindication voltage V_(THM) with the fifth threshold TH5. If theindication voltage V_(THM) is less than the fifth threshold TH5, thenthe flowchart 900 goes to step 906; otherwise, it returns to step 902.

At step 906, if the control logic circuit 226 detects that theindication voltage V_(THM) is less than the fifth threshold TH5 for aspecified time interval, then the flowchart 900 goes to step 908;otherwise, it goes to step 904.

At step 908, the control logic circuit 226 determines that a shortcircuit is present in the temperature sensor 260.

At step 910, the control logic circuit 226 obtains information for theindication voltage V_(THM) from the signal 232, and compares theindication voltage V_(THM) with the sixth threshold TH6. If theindication voltage V_(THM) is greater than the sixth threshold TH6, thenthe flowchart 900 goes to step 912; otherwise, it returns to step 902.

At step 912, if the control logic circuit 226 detects that theindication voltage VTHM is greater than the sixth threshold TH6 for aspecified time interval, then the flowchart 900 goes to step 914;otherwise, it goes to step 910.

At step 914, the control logic circuit 226 determines that an opencircuit is present in the temperature sensor 260.

Although FIG. 9 shows that steps 904 and 910 are performed in parallel,the invention is not so limited. In another embodiment, the BMS 204 canperform step 910 before or after performing step 904. For example, atstep 904, if the indication voltage V_(THM) is not less than the fifththreshold TH5, then the flowchart goes to step 910; otherwise, it goesto step 906. For another example, at step 910, if the indication voltageV_(THM) is not greater than the sixth threshold TH6, then the flowchartgoes to step 904; otherwise, it goes to step 912.

FIG. 10 illustrates a circuit diagram of an example of a battery pack1000, in an embodiment of the present invention. FIG. 10 is described incombination with FIG. 2A and FIG. 2B. As shown in FIG. 10, the batterypack 1000 includes a low-pass filter 1006 and a BMS 1004. The BMS 1004can be powered by the battery cells 202 through the low-pass filter1006. In an embodiment, the BMS 1004 can also include circuits similarto the status detection circuit 262′ and the fault detection circuit264′ in FIG. 2B.

As shown in FIG. 10, the low-pass filter 1006 includes a resistivecomponent RF, e.g., a filter resistor, coupled between a positiveterminal of the battery cells 202 and a connection node N₀, and a filtercapacitor C₀ coupled between the connection node N₀ and ground. In anembodiment, the BMS 1004 can perform the status detection functionsdescribed above in relation to FIG. 2A and FIG. 2B. The BMS 1004 canalso, but not necessarily, perform the fault detection functionsdescribed above in relation to FIG. 2A and FIG. 2B. Additionally, theBMS 1004 can include a fifth detection circuit (e.g., including amultiplexer circuit 1034, an ADC 1066, and a control logic circuit 1026)that receives a battery voltage V_(BAT) at the positive terminal of thebattery cells 202, receives a supply voltage V_(CC) from the batterycells 202 through the connection node No₀, and detects whether a faultis present in the BMS 1004 according to the difference between thebattery voltage V_(BAT) and the supply voltage V_(CC).

More specifically, in an embodiment, the BMS 1004 is powered by a supplycurrent I_(CC) through the power supply pin VCC of the BMS 1004. Becausethe supply current I_(CC) flows through the resistive component RF, avoltage V_(BAT)-V_(CC) across the resistive component R_(F) represents,e.g., is linearly proportional to, the supply current I_(CC). Thus, thesupply current I_(CC) that powers the BMS 1004 can be estimated by:I_(CC)=(V_(BAT)-V_(CC))/R_(F). In an embodiment, the BMS 1004 has anoperating range for the supply current I_(CC). If the supply currentI_(CC) exceeds the maximum current of the operating range, it canindicate that a fault, e.g., a short circuit, is present in one or morecomponents powered by a power regulator, e.g., a voltage regulator, inthe BMS 1004. Thus, in an embodiment, if the difference between thebattery voltage V_(BAT) and the supply voltage V_(CC) is greater than aseventh threshold TH7 (which may also be referred to as a voltagedifference threshold), e.g., indicating that the supply current I_(CC)is greater than a safe current threshold and indicating that powerconsumed by the BMS 1004 exceeds a safe threshold, then the fifthdetection circuit can determine that a fault, e.g., a short circuit, ispresent in the BMS 1004. Accordingly, the BMS 1004 can stopcharging/discharging the battery pack 1004.

In an embodiment, the seventh threshold TH7 represents a safe currentthreshold that is greater than the maximum current level of theoperating range for the supply current I_(CC).

In summary, embodiments according to the present invention providesolutions to detect faults, e.g., including short circuit and/or opencircuit, in battery packs. For example, if a BMS in the battery packdetects that a rate of change dV_(PACK)/dt at a positive terminal PACK+of the battery pack is greater than a first threshold for apredetermined time interval, and the BMS does not detect an OCcondition, then the BMS can determine that a short circuit is present ina battery current sensor in the battery pack. For another example, ifthe BMS detects that an R_(DS(ON)) voltage of a discharge switch of thebattery pack is greater than a second threshold for a preset timeinterval, and the BMS does not detect an OC condition, then the BMS candetermine that a short circuit is present in the battery current sensor.For yet another example, the BMS can generate identical currents to flowthrough identical filter resistors coupled between the current sensingpins ISP and ISN and the battery current sensor, such that the voltagesat the sensing pins ISP and ISN not only can represent the batterycurrent when the pins ISP and ISN are well-connected to the currentsensor, but also can represent an open circuit at the pin ISP or ISNwhen the pin ISP or ISN is not well-connected to the current sensor. Foryet another example, the BMS can compare an indication voltage on atemperature sensor with a fifth threshold that represents a shortcircuit in the temperature sensor, and compare the indication voltagewith a sixth threshold that represents an open circuit in thetemperature sensor. The comparison result can indicate whether a shortcircuit or an open circuit is present in the temperature sensor. For yetanother example, the BMS can detect whether power consumed by the BMSexceeds a safe threshold by comparing a difference between a batteryvoltage and a supply voltage of the BMS with a seventh threshold. If itis detected that the power consumed by the BMS exceeds the safethreshold, then it can be determined that a short circuit is present inthe components powered by the BMS.

While the foregoing description and drawings represent embodiments ofthe present invention, it will be understood that various additions,modifications and substitutions may be made therein without departingfrom the spirit and scope of the principles of the present invention asdefined in the accompanying claims. One skilled in the art willappreciate that the invention may be used with many modifications ofform, structure, arrangement, proportions, materials, elements, andcomponents and otherwise, used in the practice of the invention, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims and theirlegal equivalents, and not limited to the foregoing description.

I claim:
 1. A battery management system comprising: a plurality ofsensors that sense statuses of a battery pack comprising a battery cellcoupled to a positive terminal of said battery pack through a printedcircuit board trace, wherein said sensors comprise a current sensor thatsenses a battery current flowing from said battery cell to said positiveterminal of said battery pack through said printed circuit board trace;status detection circuitry, coupled to said sensors, that detectswhether said battery pack is in a normal condition based on saidstatuses to generate a detection result; and fault detection circuitry,coupled to said sensors, that detects whether a fault is present in saidbattery pack, wherein said fault detection circuitry comprises a firstdetection circuit that monitors a rate of decrease of a voltage at saidpositive terminal of said battery pack, and detects whether a fault ispresent in said current sensor based on a result of a comparison betweensaid rate of decrease and a rate of change threshold and also based onsaid detection result, and wherein if said rate of decrease is greaterthan said rate of change threshold for a predetermined time interval,and if said detection result indicates that said battery current is insaid normal condition, then said status detection circuitry determinesthat a fault is present in said current sensor.
 2. The batterymanagement system of claim 1, wherein said fault in said current sensorcomprises a short circuit in said current sensor.
 3. The batterymanagement system of claim 1, wherein said battery pack comprises adischarge switch that said battery current flows through, and whereinsaid fault detection circuitry further comprises a second detectioncircuit that monitors a sense voltage across said discharge switch, anddetects whether a fault is present in said current sensor based on aresult of a comparison between said sense voltage and a sense voltagethreshold, and also based on said detection result of said statusdetection circuitry.
 4. The battery management system of claim 3,wherein if said sense voltage is greater than said sense voltagethreshold for a preset time interval, and if said status detectioncircuitry detects that said battery current is in said normal condition,then a short circuit in said current sensor is indicated.
 5. The batterymanagement system of claim 1, wherein said battery pack comprises afirst resistor coupled between a first end of said current sensor and afirst terminal of said status detection circuitry, and also comprises asecond resistor coupled between a second end of said current sensor anda second terminal of said status detection circuitry, wherein said faultdetection circuitry further comprises a detection circuit that generatesa first current through said first resistor from said first terminal tosaid first end, generates a second current through said second resistorfrom said second terminal to said second end, and detects whether afault is present at said first terminal by comparing a voltage on saidfirst resistor with a first voltage threshold and detects whether afault is present at said second terminal by comparing a voltage on saidsecond resistor with a second voltage threshold.
 6. The batterymanagement system of claim 5, wherein said first and second resistorshave substantially the same resistance, and wherein said first andsecond currents have substantially the same current level.
 7. Thebattery management system of claim 5, wherein if said voltage on saidfirst resistor is greater than said first voltage threshold, then anopen circuit at said first terminal is indicated, and wherein if saidvoltage on said second resistor is greater than said second voltagethreshold, then an open circuit at said second terminal is indicated. 8.The battery management system of claim 1, wherein said sensors furthercomprise a thermistor, coupled to said fault detection circuitry, thatgenerates an indication voltage indicative of temperature in saidbattery pack, and wherein if said fault detection circuitry detects thatsaid indication voltage is less than an indication voltage threshold fora specified time interval, then a short circuit in said thermistor isindicated.
 9. The battery management system of claim 1, wherein saidsensors further comprise a thermistor, coupled to said fault detectioncircuitry, that generates an indication voltage indicative oftemperature in said battery pack, and wherein if said fault detectioncircuitry detects that said indication voltage is greater than saidindication voltage threshold for a specified time interval, then an opencircuit in said thermistor is indicated.
 10. The battery managementsystem of claim 1, wherein said fault detection circuitry furthercomprises a second detection circuit that receives a battery voltage ata positive terminal of said battery cell in said battery pack, receivesa supply voltage for said battery management system at a connectionnode, and detects whether a fault is present in said battery managementsystem according to a difference between said battery voltage and saidsupply voltage, wherein said battery pack comprises a resistivecomponent coupled between said positive terminal of said battery celland said connection node, and wherein a current flowing from saidpositive terminal of said battery cell to said connection node throughsaid resistive component powers said battery management system.
 11. Thebattery management system of claim 10, wherein if said differencebetween said battery voltage and said supply voltage is greater than avoltage difference threshold, then a fault in said battery managementsystem is indicated.
 12. The battery management system of claim 11,wherein said fault in said battery management system comprises a shortcircuit in said battery management system.
 13. A battery packcomprising: a plurality of battery cells coupled to a positive terminalof said battery pack through a printed circuit board trace; a pluralityof sensors that sense statuses of said battery cells, said sensorscomprising a current sensor that senses a battery current flowing fromsaid battery cells to said positive terminal of said battery packthrough said printed circuit board trace; and a battery managementsystem, coupled to said battery cells and said sensors, that detectswhether said battery pack is in a normal condition based on saidstatuses to generate a detection result, and detects whether a fault ispresent in said battery pack, wherein said battery management systemcomprises a first detection circuit that monitors a rate of decrease ofa voltage at said positive terminal of said battery pack, and detectswhether a fault is present in said current sensor based on a result of acomparison between said rate of decrease and a rate of change thresholdand also based on said detection result, and wherein if said rate ofdecrease is greater than said rate of change threshold for apredetermined time interval, and if said detection result indicates thatsaid battery current is in said normal condition, then said batterymanagement system determines that a fault is present in said currentsensor.
 14. The battery pack of claim 13, wherein said fault in saidcurrent sensor comprises a short circuit in said current sensor.
 15. Thebattery pack of claim 13, wherein said battery pack comprises adischarge switch that said battery current flows through, and whereinsaid battery management system further comprises a second detectioncircuit that monitors a sense voltage across said discharge switch, anddetects whether a fault is present in said current sensor based on aresult of a comparison between said sense voltage and a sense voltagethreshold, and also based on said detection result.
 16. The battery packof claim 13, wherein said battery pack comprises a first resistorcoupled between a first end of said current sensor and a first terminalof said battery management system, and also comprises a second resistorcoupled between a second end of said current sensor and a secondterminal of said battery management system, wherein said batterymanagement system further comprises a second detection circuit thatgenerates a first current through said first resistor from said firstterminal to said first end, generates a second current through saidsecond resistor from said second terminal to said second end, anddetects whether a fault is present at said first terminal by comparing avoltage on said first resistor with a first voltage threshold anddetects whether a fault is present at said second terminal by comparinga voltage on said second resistor with a second voltage threshold. 17.The battery pack of claim 13, wherein said sensors comprise atemperature sensor that generates an indication voltage indicative oftemperature in said battery pack, and wherein said battery managementsystem further comprises a second detection circuit that detects whethera fault is present in said temperature sensor by comparing saidindication voltage with an indication voltage threshold.
 18. The batterypack of claim 13, wherein said battery management system furthercomprises a second detection circuit that receives a battery voltage ata positive terminal of said battery cells, receives a supply voltage forsaid battery management system at a connection node, and detects whethera fault is present in said battery management system according to adifference between said battery voltage and said supply voltage, whereinsaid battery pack comprises a resistive component coupled between saidpositive terminal of said battery cell and said connection node, andwherein a current flowing from said positive terminal of said batterycells to said connection node through said resistive component powerssaid battery management system.
 19. A method for detecting a fault in abattery pack, said method comprising: sensing, using a current sensor, abattery current flowing from a battery cell in said battery pack to apositive terminal of said battery pack through a printed circuit boardtrace between said battery cell and said positive terminal of saidbattery pack; detecting whether said battery pack is in a normalcondition based on statuses of said battery pack to generate a detectionresult; monitoring a rate of decrease of a voltage at said positiveterminal of said battery pack; comparing said rate of decrease with arate of change threshold; and determining whether a fault is present insaid battery current sensor, wherein said fault is present if said rateof decrease is greater than said rate of change threshold for apredetermined time interval, and if said detection result indicates thatsaid battery current is in said normal condition.
 20. The method ofclaim 19, wherein said fault in said current sensor comprises a shortcircuit in said current sensor.